The present invention relates generally to hydraulically driven valves and, more particularly, to hydraulic systems that use hydraulically driven valves.
In one class of hydraulically actuated electronically controlled fuel injectors (HEUI) such as those manufactured by Caterpillar Inc., of Peoria, Ill., a valve design is employed which precisely controls the timing and duration of fuel injection. In one version disclosed in U.S. Pat. No. 5,687,693 issued to Chen et al on Nov. 18, 1997, control of actuation fluid flow for fuel injection is achieved with a spool valve having opposing hydraulic surfaces. Although the spool valve has opposing hydraulic surfaces, it still relies upon a biasing spring to return the spool to its rest position when termination of injection is desired. While these spring biased spool valves have performed well in fuel injectors, differing demands in other hydraulic applications can render spring biasing a less than satisfactory alternative. One such example might be in control valves for gas exchange or exhaust brake actuators.
In some hydraulically actuated gas exchange valves a relatively large quantity of hydraulic fluid may be necessary to actuate the valves. In addition, this fluid must be evacuated back through the valve between events in order to reset the hydraulic devices. As a result, a significant amount of fluid must pass through the flow control valve. Where a spool valve is used, this fluid flow may create dynamic flow forces on the various surface features of the spool. In some cases, these forces necessitate a substantially greater force to return the spool to its rest position than would otherwise be necessary. Providing the necessary biasing force to completely move the spool to its rest position with a conventional biasing spring can be problematic, especially when space is limited. Furthermore, the necessity of providing space for a biasing spring can limit other aspects of valve design.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the present invention, a hydraulically driven valve includes a valve body defining a first passage and a second passage. A valve member is positioned in the valve body and is movable between a first position in which the first passage is open to the second passage, and a second position in which the first passage is closed to the second passage. The valve member has a biasing hydraulic surface and a control hydraulic surface. A biasing pressure chamber is defined at least in part by the valve body and the valve member""s biasing hydraulic surface. Also located within the valve body is a control hydraulic chamber defined at least in part by the valve body and the valve member""s control hydraulic surface. The biasing pressure chamber and the control pressure chamber are fluidly isolated from the first passage and the second passage. A medium pressure force acts on the biasing hydraulic surface whereas either a high pressure or a low pressure force acts on the control hydraulic surface.
In another aspect of the present invention, a method of operating a valve includes the steps of providing a hydraulically driven valve that includes a valve body defining a first passage and a second passage. A valve member is positioned in the valve body and includes a biasing hydraulic surface and a control hydraulic surface. The biasing hydraulic surface and the control hydraulic surface are fluidly isolated from the first passage and the second passage. The valve member is then hydraulically driven toward a first position that opens the first passage to the second passage, or toward a second position that closes the first passage to the second passage.
In still another aspect of the present invention, a hydraulic system includes a source of high pressure fluid, a source of low pressure fluid, and at least one hydraulic device. Also provided is a hydraulically driven valve that includes a valve body that defines a first passage and a second passage. The hydraulically driven valve also provides a valve member positioned in the valve body that has a biasing hydraulic surface and a control hydraulic surface. Further, the hydraulic system includes a biasing pressure chamber defined at least in part by the valve body and the biasing hydraulic surface, and a control pressure chamber defined at least in part by the valve body and the control hydraulic surface. The biasing pressure chamber and the control pressure chamber are fluidly isolated from the first passage and the second passage. A medium pressure force acts on the biasing hydraulic surface. Also provided is a pilot valve having a first position in which the control pressure chamber is fluidly connected to the source of high pressure fluid, and a second position in which the control pressure chamber is fluidly connected to the low pressure fluid.